1. Field of the Invention
The present invention relates generally to disk drives such as CD-ROM (Compact Disk-Read Only Memory) drives, and more particularly, to a method for reducing read errors when reading data with a disk drive.
2. Description of the Related Art
Since a CD-ROM drive used in a contemporary personal computer or workstation accesses data at high speed such as 16.times. or 24.times. speed, read errors are likely to occur. Such a high-speed disk drive is designed to perform read retry processing that repeatedly attempts to read upon detecting a read error. Methods for the read retry processing are as follows: (1) a general method to retry reading for a prescribed number of times under the condition that the number of disk revolutions per unit time (i.e., disk revolution rate) is maintained at a given level; (2) a temporary decelerating method for reattempting to read by decreasing the disk revolution rate if an error is not corrected by the first general method, and for returning to the original disk revolution rate if the disk drive succeeds in reading; and (3) a decelerating method for reattempting to read by decreasing the disk revolution rate if an error is not corrected by the first general method, and for maintaining the revolution rate at the decreased level if the disk drive successfully reads.
The above methods for read retry processing have respective advantages and disadvantages. The first general method exhibits low error correcting capability because the disk revolution rate is always maintained at a given level. The second temporary decelerating method is superior in error correcting capability, but increases the load on the system. That is, the revolution of a spindle motor is frequently controlled, due to a frequent abrupt increase in the disk revolution rate to return to the original revolution rate after a corresponding abrupt decrease the revolution rate to overcome an error. Furthermore, the second temporary decelerating method may damage the disk because the disk returns to the original revolution rate after an error is corrected. Typically, the disk is damaged due to the abrupt changes in the revolution speed of the disk. The damaged part of the disk may generate a read error again and therefore it becomes difficult to decipher the data in the error-prone region. In the third decelerating method, the data transmission rate is lowered because the decreased disk revolution rate is maintained after an error occurs.